The present invention relates, generally, to breathing apparatuses, such as hoods of the type to protect the wearer's head and respiratory system during escape from smoke or dangerous fumes, and, more particularly, to such a hood which is provided with a silicone neck “dam” or seal having a coating of parylene to thereby reduce permeability of the neck dam by nuclear, biological, chemical/chemical, biological, radiological (“NBC/CBR”) warfare agents.